Welding of an element of a track unit and a rail section without adding any material

ABSTRACT

The stretch of rail comprises a railway switch element ( 12 ) made from high-alloy steel, in which at least one alloy element has a content equal to at least 5% by weight, and a length of rail ( 14 ) made from steel, connected to one another by a weld without deposition of metal. The length of rail ( 14 ) is formed from a medium-alloy low-carbon steel of which the carbon content is less than 0.55% by weight.

The present invention relates to a stretch of rail of the typecomprising a railway switch element made from high-alloy steel, in whichat least one alloy element has a content equal to at least 5% by weight,and a length of steel rail, connected to one another by a weld withoutdeposition of metal.

The invention relates in particular to the connection between a switchsuch as a crossing frog and a section of rail consisting for example ofa running line rail made from carbon steel.

It is known that, when a part made from carbon steel is welded to a partmade from high-alloy steel the fusion produced during this operationcauses, at the interface between the two parts, the formation of alloysof which the chemical composition is different from that of the basicmaterials. When the welding is done without deposition of metal, forexample by flash welding, it is difficult to control the nature of thealloys created. Therefore, the weld produced is generally of mediocrequality, rather more like glueing.

The carbon rails currently used to make the rails of running linesinclude a quantity of carbon of between 0.55% and 0.8% by weight. Inorder to ensure a sufficient hardness, the rails have additions of othermetals such as chromium. However, the high quantity of chromium makeswelding impossible between two steels which are too highly alloyed.

In order to solve the problem mentioned above, it is known to provide aninsert forming an intermediate part between the railway switch elementmade from high-alloy steel and the length of rail. This intermediatepart is formed from a material capable of being welded easily onto therailway switch element on the one hand and onto the length of rail onthe other hand.

The use of such an intermediate part increases the cost of implementingthe connection process, particularly because of the specificcharacteristics of the material forming the insert and the necessity ofproviding two welds. Moreover, falls in hardness are observed in thelength of rail, in the zone heat-affected by the energy of the welding.

The object of the invention is to propose a solution which makes itpossible to ensure a satisfactory level of hardness of the switchelement and of the length of rail, and also of the connection betweenthe switch element and the length of rail, without increasing the costof producing the connection between them.

To this end, the invention relates to a stretch of rail of theaforementioned type, characterised in that the length of rail is formedfrom a low-carbon steel in which the carbon content is less than 0.55%by weight.

According to particular embodiments, the stretch of rail has one or moreof the following characteristics:

the length of rail is formed from a low-carbon steel of which themedium-alloy carbon content is less than 0.5% by weight;

the medium-alloy low-carbon steel forming the length of rail is abainitic steel;

the medium-alloy low-carbon steel forming the length of rail has thefollowing composition by weight:

-   -   0.05% to 0.50% of carbon;    -   0.5% to 2.5% of manganese;    -   0.6% to 3% of silicon or aluminium;    -   0.25% to 3.1% of chromium; and    -   0% to 0.9% of molybdenum;

the medium-alloy low-carbon steel forming the length of rail has acomposition defined below:

-   -   0.28% to 0.36% of carbon;    -   1.40% to 1.70% of manganese;    -   at most 0.03% of phosphorus;    -   0.01% to 0.03% of sulphur;    -   at most 0.005% of aluminium;    -   1% to 1.40% of silicon;    -   0.40% to 0.60% of chromium;    -   0.08% to 0.20% of molybdenum;    -   at most 0.04% of titanium; and    -   at most 0.004% of boron; and

the railway switch element made from high-alloy steel comprises 12% to14% by weight of manganese.

The invention will be better understood by reading the description whichfollows, given solely by way of example and with reference to thedrawings, in which:

FIG. 1 is a schematic view in elevation of a railway track crossing frogto which four lengths of running line rail are welded;

FIG. 2 is a photomicrograph of a weld of a stretch of rail according tothe invention; and

FIGS. 3 and 4 are diagrams showing the hardness measured along thelength of the stretch of rail in the region of the weld for twodifferent embodiments of the invention.

FIG. 1 shows a crossing frog which permits the crossing of twointersecting stretches of track. Thus the crossing frog 12 is connectedat its four ends to four lengths of running line 14.

The lengths of line 14 are connected to the frog by welds 16 withoutdeposition of metal.

As is known per se, the crossing frog 12 is formed from a high-alloysteel, particularly a steel in which at least one alloy element has acontent equal to at least 5% by weight.

This steel is in particular an alloyed steel containing between 12% and14% by weight of manganese, the crossing frog having been produced bymoulding. This is a steel which is well known under the name ofHADFIELD.

The hardness of this steel is between 170 and 230 HB.

According to the invention, the lengths of rail 14 are made from amedium-alloy low-carbon steel of which the carbon content is less than0.55% by weight, and each weld 16 is a weld without deposition of metalproduced directly between the high-alloy steel and the medium-alloylow-carbon steel. The carbon content of the medium-alloy low-carbonsteel is preferably less than 0.5% by weight.

The medium-alloy low-carbon steel is preferably a bainitic steel withoutcarbide.

The low-carbon bainitic steel forming the length of rail 14 hasadvantageously the following composition by weight:

-   -   0.05% to 0.50% of carbon;    -   0.5% to 2.5% of manganese;    -   0.6% to 3% of silicon or aluminium;    -   0.25% to 3.1% of chromium; and    -   0% to 0.9% of molybdenum.

Even more preferably, the bainitic steel has a composition definedbelow:

-   -   0.28% to 0.36% of carbon;    -   1.40% to 1.70% of manganese;    -   at most 0.03% of phosphorus;    -   0.01% to 0.03% of sulphur;    -   at most 0.005% of aluminium;    -   1% to 1.40% of silicon;    -   0.40% to 0.60% of chromium;    -   0.08% to 0.20% of molybdenum;    -   at most 0.04% of titanium; and    -   at most 0.004% of boron.

This steel has a hardness of between 350 and 390 HB.

The weld 16 is obtained for example by flash welding and forgingaccording to a conventional welding cycle which is known per se.

As a variant, the weld can be obtained by induction, by friction, byelectron beams, by laser or by any other high-energy beam.

The appearance of the weld 16 which is obtained is illustrated in FIG.2. On this microphotograph which is enlarged five hundred times itappears that the interface is very neat between the low-carbon bainiticsteel and the high-alloy steel, the two steels being interpenetrated ina satisfactory manner.

According to a first embodiment which is envisaged, the switch elementmade from high-alloy steel is at ambient temperature before the flashwelding and has a hardness resulting from re-annealing of 170 to 230 HB.

In this case the development of the hardness of the stretch of rail inthe vicinity of the weld is shown in FIG. 3.

It is observed that, in its running part, the length of rail 14 has ahardness of between 290 and 330 HB and that this hardness increases toreach a value close to 380 HB in the immediate vicinity of the weld. Thehardness of the stretch of rail remains at a value of between 185 and235 HB in the switch element 12 made from high-alloy steel. Thishardness corresponds to the hardness of the switch element beforewelding.

Therefore it is observed that with the compositions according to theinvention the hardness remains satisfactory in the immediate vicinity ofthe weld, and is not less than the hardness specific to the two elementswhich are welded to one another, and that in particular there is no dropin the hardness in the heat-affected zone (HAZ).

According to a variant, the end of the switch element made fromhigh-alloy steel which is intended to be welded is pre-hardened beforethe flash welding is carried out in order to increase its hardness. Thispre-hardening is obtained for example by explosion.

Thus the hardness of the switch element before welding is brought to avalue of between 330 and 360 HB.

With this additional step, the measurements of hardness obtained arethose illustrated in FIG. 4. In this case, the hardness of the length ofrail is substantially identical to that of FIG. 3. By contrast, thehardness of the switch element made from high-alloy steel in theimmediate vicinity of the weld is substantially equal to 350 HB, a valuesubstantially equal to that of the length of rail in its runningportion.

1. Stretch of rail comprising a railway switch element (12) made fromhigh-alloy steel, in which at least one alloy element has a contentequal to at least 5% by weight, and a length of rail (14) made frommedium-alloy steel, directly connected to one another by a weld withoutdeposition of metal, characterised in that the length of rail (14) isformed from a medium-alloy low-carbon steel in which the carbon contentis less than 0.55% by weight.
 2. Stretch of rail as claimed in claim 1,characterised in that the length of rail (14) is formed from amedium-alloy low-carbon steel in which the carbon content is less than0.5% by weight.
 3. Stretch of rail as claimed in claim 1, characterisedin that medium-alloy low-carbon steel forming the length of rail is abainitic steel.
 4. Stretch of rail as claimed in claim 3, characterisedin that the medium-alloy low-carbon steel is a bainitic steel withoutcarbide.
 5. Stretch of rail as claimed in claim 1, characterised in thatthe medium-alloy low-carbon steel forming the length of rail has thefollowing composition by weight: 0.05% to 0.50% of carbon; 0.5% to 2.5%of manganese; 0.6% to 3% of silicon or aluminium; 0.25% to 3.1% ofchromium; and 0% to 0.9% of molybdenum.
 6. Stretch of rail as claimed inclaim 5, characterised in that the medium-alloy low-carbon steel formingthe length of rail has a composition defined below: 0.28% to 0.36% ofcarbon; 1.40% to 1.70% of manganese; at most 0.03% of phosphorus; 0.01%to 0.03% of sulphur; at most 0.005% of aluminium; 1% to 1.40% ofsilicon; 0.40% to 0.60% of chromium; 0.08% to 0.20% of molybdenum; atmost 0.04% of titanium; and at most 0.004% of boron.
 7. Stretch of railas claimed in claim 1, characterised in that the railway switch elementmade from high-alloy steel comprises 12% to 14% by weight of manganese.